1. Field of the Invention
The invention relates to an active matrix display device which comprises a plurality of pixels arranged in a matrix with columns and rows, a plurality of source lines corresponding to the pixels on the columns, a plurality of gate lines corresponding to the pixels on the rows, and a common line coupled to all of the pixels power supply device, and more particularly to an electronic device comprising the active matrix display device.
2. Description of the Related Art
Alignment of liquid crystal molecules varies with variations in voltage applied thereto. A liquid crystal display (LCD) displays images by using the characteristics of the liquid crystal molecules and by transmitting/obstructing external light or backlight light. Generally, LCDs comprise transmissive type LCDs, in which a backlight at the back of a display serves as a light source for displaying, reflective type LCDs, in which external light is reflected for displaying without any backlight source, and trans-reflective type LCDs, in which a backlight source and light which is reflected from external light are used for displaying.
Transmissive type LCDs can advantageously display images with higher chroma, and users can easily view images in a dark environment. However, transmissive type LCDs consume much power due to the required backlight source, and dark images occur under bright environments. Meanwhile, reflective type LCDs advantageously consume less power and users can easily view images in a bright environment. However, reflective type LCDs display image with lower chroma, and users can not easily view images in a dark environment. Thus, trans-reflective type LCDs have grown in popularity. For trans-reflective type LCDs, each pixel is divided into at least one pair of sub-pixels which are used respectively for light transmission and light reflection.
In addition, trans-reflective type LCDs have two modes when voltage is not supplied thereto: a normally white mode in which the LCD displays white; or a normally black mode in which the LCD displays black. Particularly, a vertical alignment (VA) LCD usually uses the normally black mode. However, color shift usually occurs for VA LCDs when in the normally black mode. That is, contrast varies with the different viewing angles of users.
Currently, a method for solving the above problem is to divide one pixel into a plurality of sub-pixels and apply different voltages to each sub-pixel. The sub-pixels display different degrees of brightness in response to the different applied voltages. Since the different degrees of brightness induce an averaging brightness result for eyes of users, the brightness problem is improved, and color shift is eliminated.
Accordingly, when one pixel is divided into a plurality of sub-pixels, a plurality of voltages applied to the sub-pixels are required.
Conventional techniques provide approaches to apply a plurality of voltages to each pixel. One approach is to dispose a plurality of gate lines and source lines to provide different voltages to each element, as shown in non-patent REFERENCE 1. Another approach is to dispose an impedance element, such as a capacitor, coupled to a liquid crystal unit in a particular sub-pixel in parallel and apply a different voltage to the liquid crystal unit of the particular sub-pixel from voltages applied to the liquid crystal units of the other sub-pixels, as shown in non-patent REFERENCE 2.
[REFERENCE 1]: ┌Novel TFT-LCD Technology for Motion-blur Reducing Using 120-Hz Driving with McFi┘, S-S. Kim, Section 18.1, SID07 Digest, pages 1003˜1006.
[REFERENCE 2]: ┌MVA-LCD with Low Color Shift and High Image Quality┘, M-C. Tai, Section 18.2, SID07 Digest, pages 1007˜1009.